1 /*
   2  * Copyright (c) 2001, 2011, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTORPOLICY_HPP
  26 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTORPOLICY_HPP
  27 
  28 #include "gc_implementation/g1/collectionSetChooser.hpp"
  29 #include "gc_implementation/g1/g1MMUTracker.hpp"
  30 #include "memory/collectorPolicy.hpp"
  31 
  32 // A G1CollectorPolicy makes policy decisions that determine the
  33 // characteristics of the collector.  Examples include:
  34 //   * choice of collection set.
  35 //   * when to collect.
  36 
  37 class HeapRegion;
  38 class CollectionSetChooser;
  39 
  40 // Yes, this is a bit unpleasant... but it saves replicating the same thing
  41 // over and over again and introducing subtle problems through small typos and
  42 // cutting and pasting mistakes. The macros below introduces a number
  43 // sequnce into the following two classes and the methods that access it.
  44 
  45 #define define_num_seq(name)                                                  \
  46 private:                                                                      \
  47   NumberSeq _all_##name##_times_ms;                                           \
  48 public:                                                                       \
  49   void record_##name##_time_ms(double ms) {                                   \
  50     _all_##name##_times_ms.add(ms);                                           \
  51   }                                                                           \
  52   NumberSeq* get_##name##_seq() {                                             \
  53     return &_all_##name##_times_ms;                                           \
  54   }
  55 
  56 class MainBodySummary;
  57 
  58 class PauseSummary: public CHeapObj {
  59   define_num_seq(total)
  60     define_num_seq(other)
  61 
  62 public:
  63   virtual MainBodySummary*    main_body_summary()    { return NULL; }
  64 };
  65 
  66 class MainBodySummary: public CHeapObj {
  67   define_num_seq(satb_drain) // optional
  68   define_num_seq(parallel) // parallel only
  69     define_num_seq(ext_root_scan)
  70     define_num_seq(mark_stack_scan)
  71     define_num_seq(update_rs)
  72     define_num_seq(scan_rs)
  73     define_num_seq(obj_copy)
  74     define_num_seq(termination) // parallel only
  75     define_num_seq(parallel_other) // parallel only
  76   define_num_seq(mark_closure)
  77   define_num_seq(clear_ct)  // parallel only
  78 };
  79 
  80 class Summary: public PauseSummary,
  81                public MainBodySummary {
  82 public:
  83   virtual MainBodySummary*    main_body_summary()    { return this; }
  84 };
  85 
  86 class G1CollectorPolicy: public CollectorPolicy {
  87 protected:
  88   // The number of pauses during the execution.
  89   long _n_pauses;
  90 
  91   // either equal to the number of parallel threads, if ParallelGCThreads
  92   // has been set, or 1 otherwise
  93   int _parallel_gc_threads;
  94 
  95   enum SomePrivateConstants {
  96     NumPrevPausesForHeuristics = 10
  97   };
  98 
  99   G1MMUTracker* _mmu_tracker;
 100 
 101   void initialize_flags();
 102 
 103   void initialize_all() {
 104     initialize_flags();
 105     initialize_size_info();
 106     initialize_perm_generation(PermGen::MarkSweepCompact);
 107   }
 108 
 109   virtual size_t default_init_heap_size() {
 110     // Pick some reasonable default.
 111     return 8*M;
 112   }
 113 
 114   double _cur_collection_start_sec;
 115   size_t _cur_collection_pause_used_at_start_bytes;
 116   size_t _cur_collection_pause_used_regions_at_start;
 117   size_t _prev_collection_pause_used_at_end_bytes;
 118   double _cur_collection_par_time_ms;
 119   double _cur_satb_drain_time_ms;
 120   double _cur_clear_ct_time_ms;
 121   bool   _satb_drain_time_set;
 122 
 123 #ifndef PRODUCT
 124   // Card Table Count Cache stats
 125   double _min_clear_cc_time_ms;         // min
 126   double _max_clear_cc_time_ms;         // max
 127   double _cur_clear_cc_time_ms;         // clearing time during current pause
 128   double _cum_clear_cc_time_ms;         // cummulative clearing time
 129   jlong  _num_cc_clears;                // number of times the card count cache has been cleared
 130 #endif
 131 
 132   // Statistics for recent GC pauses.  See below for how indexed.
 133   TruncatedSeq* _recent_rs_scan_times_ms;
 134 
 135   // These exclude marking times.
 136   TruncatedSeq* _recent_pause_times_ms;
 137   TruncatedSeq* _recent_gc_times_ms;
 138 
 139   TruncatedSeq* _recent_CS_bytes_used_before;
 140   TruncatedSeq* _recent_CS_bytes_surviving;
 141 
 142   TruncatedSeq* _recent_rs_sizes;
 143 
 144   TruncatedSeq* _concurrent_mark_remark_times_ms;
 145   TruncatedSeq* _concurrent_mark_cleanup_times_ms;
 146 
 147   Summary*           _summary;
 148 
 149   NumberSeq* _all_pause_times_ms;
 150   NumberSeq* _all_full_gc_times_ms;
 151   double _stop_world_start;
 152   NumberSeq* _all_stop_world_times_ms;
 153   NumberSeq* _all_yield_times_ms;
 154 
 155   size_t     _region_num_young;
 156   size_t     _region_num_tenured;
 157   size_t     _prev_region_num_young;
 158   size_t     _prev_region_num_tenured;
 159 
 160   NumberSeq* _all_mod_union_times_ms;
 161 
 162   int        _aux_num;
 163   NumberSeq* _all_aux_times_ms;
 164   double*    _cur_aux_start_times_ms;
 165   double*    _cur_aux_times_ms;
 166   bool*      _cur_aux_times_set;
 167 
 168   double* _par_last_gc_worker_start_times_ms;
 169   double* _par_last_ext_root_scan_times_ms;
 170   double* _par_last_mark_stack_scan_times_ms;
 171   double* _par_last_update_rs_times_ms;
 172   double* _par_last_update_rs_processed_buffers;
 173   double* _par_last_scan_rs_times_ms;
 174   double* _par_last_obj_copy_times_ms;
 175   double* _par_last_termination_times_ms;
 176   double* _par_last_termination_attempts;
 177   double* _par_last_gc_worker_end_times_ms;
 178   double* _par_last_gc_worker_times_ms;
 179 
 180   // indicates whether we are in full young or partially young GC mode
 181   bool _full_young_gcs;
 182 
 183   // if true, then it tries to dynamically adjust the length of the
 184   // young list
 185   bool _adaptive_young_list_length;
 186   size_t _young_list_target_length;
 187   size_t _young_list_fixed_length;
 188   size_t _prev_eden_capacity; // used for logging
 189 
 190   // The max number of regions we can extend the eden by while the GC
 191   // locker is active. This should be >= _young_list_target_length;
 192   size_t _young_list_max_length;
 193 
 194   size_t _young_cset_length;
 195   bool   _last_young_gc_full;
 196 
 197   unsigned              _full_young_pause_num;
 198   unsigned              _partial_young_pause_num;
 199 
 200   bool                  _during_marking;
 201   bool                  _in_marking_window;
 202   bool                  _in_marking_window_im;
 203 
 204   SurvRateGroup*        _short_lived_surv_rate_group;
 205   SurvRateGroup*        _survivor_surv_rate_group;
 206   // add here any more surv rate groups
 207 
 208   double                _gc_overhead_perc;
 209 
 210   double _reserve_factor;
 211   size_t _reserve_regions;
 212 
 213   bool during_marking() {
 214     return _during_marking;
 215   }
 216 
 217   // <NEW PREDICTION>
 218 
 219 private:
 220   enum PredictionConstants {
 221     TruncatedSeqLength = 10
 222   };
 223 
 224   TruncatedSeq* _alloc_rate_ms_seq;
 225   double        _prev_collection_pause_end_ms;
 226 
 227   TruncatedSeq* _pending_card_diff_seq;
 228   TruncatedSeq* _rs_length_diff_seq;
 229   TruncatedSeq* _cost_per_card_ms_seq;
 230   TruncatedSeq* _fully_young_cards_per_entry_ratio_seq;
 231   TruncatedSeq* _partially_young_cards_per_entry_ratio_seq;
 232   TruncatedSeq* _cost_per_entry_ms_seq;
 233   TruncatedSeq* _partially_young_cost_per_entry_ms_seq;
 234   TruncatedSeq* _cost_per_byte_ms_seq;
 235   TruncatedSeq* _constant_other_time_ms_seq;
 236   TruncatedSeq* _young_other_cost_per_region_ms_seq;
 237   TruncatedSeq* _non_young_other_cost_per_region_ms_seq;
 238 
 239   TruncatedSeq* _pending_cards_seq;
 240   TruncatedSeq* _scanned_cards_seq;
 241   TruncatedSeq* _rs_lengths_seq;
 242 
 243   TruncatedSeq* _cost_per_byte_ms_during_cm_seq;
 244 
 245   TruncatedSeq* _young_gc_eff_seq;
 246 
 247   TruncatedSeq* _max_conc_overhead_seq;
 248 
 249   bool   _using_new_ratio_calculations;
 250   size_t _min_desired_young_length; // as set on the command line or default calculations
 251   size_t _max_desired_young_length; // as set on the command line or default calculations
 252 
 253   size_t _recorded_young_regions;
 254   size_t _recorded_non_young_regions;
 255   size_t _recorded_region_num;
 256 
 257   size_t _free_regions_at_end_of_collection;
 258 
 259   size_t _recorded_rs_lengths;
 260   size_t _max_rs_lengths;
 261 
 262   size_t _recorded_marked_bytes;
 263   size_t _recorded_young_bytes;
 264 
 265   size_t _predicted_pending_cards;
 266   size_t _predicted_cards_scanned;
 267   size_t _predicted_rs_lengths;
 268   size_t _predicted_bytes_to_copy;
 269 
 270   double _predicted_survival_ratio;
 271   double _predicted_rs_update_time_ms;
 272   double _predicted_rs_scan_time_ms;
 273   double _predicted_object_copy_time_ms;
 274   double _predicted_constant_other_time_ms;
 275   double _predicted_young_other_time_ms;
 276   double _predicted_non_young_other_time_ms;
 277   double _predicted_pause_time_ms;
 278 
 279   double _vtime_diff_ms;
 280 
 281   double _recorded_young_free_cset_time_ms;
 282   double _recorded_non_young_free_cset_time_ms;
 283 
 284   double _sigma;
 285   double _expensive_region_limit_ms;
 286 
 287   size_t _rs_lengths_prediction;
 288 
 289   size_t _known_garbage_bytes;
 290   double _known_garbage_ratio;
 291 
 292   double sigma() {
 293     return _sigma;
 294   }
 295 
 296   // A function that prevents us putting too much stock in small sample
 297   // sets.  Returns a number between 2.0 and 1.0, depending on the number
 298   // of samples.  5 or more samples yields one; fewer scales linearly from
 299   // 2.0 at 1 sample to 1.0 at 5.
 300   double confidence_factor(int samples) {
 301     if (samples > 4) return 1.0;
 302     else return  1.0 + sigma() * ((double)(5 - samples))/2.0;
 303   }
 304 
 305   double get_new_neg_prediction(TruncatedSeq* seq) {
 306     return seq->davg() - sigma() * seq->dsd();
 307   }
 308 
 309 #ifndef PRODUCT
 310   bool verify_young_ages(HeapRegion* head, SurvRateGroup *surv_rate_group);
 311 #endif // PRODUCT
 312 
 313   void adjust_concurrent_refinement(double update_rs_time,
 314                                     double update_rs_processed_buffers,
 315                                     double goal_ms);
 316 
 317 protected:
 318   double _pause_time_target_ms;
 319   double _recorded_young_cset_choice_time_ms;
 320   double _recorded_non_young_cset_choice_time_ms;
 321   bool   _within_target;
 322   size_t _pending_cards;
 323   size_t _max_pending_cards;
 324 
 325 public:
 326 
 327   void set_region_short_lived(HeapRegion* hr) {
 328     hr->install_surv_rate_group(_short_lived_surv_rate_group);
 329   }
 330 
 331   void set_region_survivors(HeapRegion* hr) {
 332     hr->install_surv_rate_group(_survivor_surv_rate_group);
 333   }
 334 
 335 #ifndef PRODUCT
 336   bool verify_young_ages();
 337 #endif // PRODUCT
 338 
 339   double get_new_prediction(TruncatedSeq* seq) {
 340     return MAX2(seq->davg() + sigma() * seq->dsd(),
 341                 seq->davg() * confidence_factor(seq->num()));
 342   }
 343 
 344   size_t young_cset_length() {
 345     return _young_cset_length;
 346   }
 347 
 348   void record_max_rs_lengths(size_t rs_lengths) {
 349     _max_rs_lengths = rs_lengths;
 350   }
 351 
 352   size_t predict_pending_card_diff() {
 353     double prediction = get_new_neg_prediction(_pending_card_diff_seq);
 354     if (prediction < 0.00001)
 355       return 0;
 356     else
 357       return (size_t) prediction;
 358   }
 359 
 360   size_t predict_pending_cards() {
 361     size_t max_pending_card_num = _g1->max_pending_card_num();
 362     size_t diff = predict_pending_card_diff();
 363     size_t prediction;
 364     if (diff > max_pending_card_num)
 365       prediction = max_pending_card_num;
 366     else
 367       prediction = max_pending_card_num - diff;
 368 
 369     return prediction;
 370   }
 371 
 372   size_t predict_rs_length_diff() {
 373     return (size_t) get_new_prediction(_rs_length_diff_seq);
 374   }
 375 
 376   double predict_alloc_rate_ms() {
 377     return get_new_prediction(_alloc_rate_ms_seq);
 378   }
 379 
 380   double predict_cost_per_card_ms() {
 381     return get_new_prediction(_cost_per_card_ms_seq);
 382   }
 383 
 384   double predict_rs_update_time_ms(size_t pending_cards) {
 385     return (double) pending_cards * predict_cost_per_card_ms();
 386   }
 387 
 388   double predict_fully_young_cards_per_entry_ratio() {
 389     return get_new_prediction(_fully_young_cards_per_entry_ratio_seq);
 390   }
 391 
 392   double predict_partially_young_cards_per_entry_ratio() {
 393     if (_partially_young_cards_per_entry_ratio_seq->num() < 2)
 394       return predict_fully_young_cards_per_entry_ratio();
 395     else
 396       return get_new_prediction(_partially_young_cards_per_entry_ratio_seq);
 397   }
 398 
 399   size_t predict_young_card_num(size_t rs_length) {
 400     return (size_t) ((double) rs_length *
 401                      predict_fully_young_cards_per_entry_ratio());
 402   }
 403 
 404   size_t predict_non_young_card_num(size_t rs_length) {
 405     return (size_t) ((double) rs_length *
 406                      predict_partially_young_cards_per_entry_ratio());
 407   }
 408 
 409   double predict_rs_scan_time_ms(size_t card_num) {
 410     if (full_young_gcs())
 411       return (double) card_num * get_new_prediction(_cost_per_entry_ms_seq);
 412     else
 413       return predict_partially_young_rs_scan_time_ms(card_num);
 414   }
 415 
 416   double predict_partially_young_rs_scan_time_ms(size_t card_num) {
 417     if (_partially_young_cost_per_entry_ms_seq->num() < 3)
 418       return (double) card_num * get_new_prediction(_cost_per_entry_ms_seq);
 419     else
 420       return (double) card_num *
 421         get_new_prediction(_partially_young_cost_per_entry_ms_seq);
 422   }
 423 
 424   double predict_object_copy_time_ms_during_cm(size_t bytes_to_copy) {
 425     if (_cost_per_byte_ms_during_cm_seq->num() < 3)
 426       return 1.1 * (double) bytes_to_copy *
 427         get_new_prediction(_cost_per_byte_ms_seq);
 428     else
 429       return (double) bytes_to_copy *
 430         get_new_prediction(_cost_per_byte_ms_during_cm_seq);
 431   }
 432 
 433   double predict_object_copy_time_ms(size_t bytes_to_copy) {
 434     if (_in_marking_window && !_in_marking_window_im)
 435       return predict_object_copy_time_ms_during_cm(bytes_to_copy);
 436     else
 437       return (double) bytes_to_copy *
 438         get_new_prediction(_cost_per_byte_ms_seq);
 439   }
 440 
 441   double predict_constant_other_time_ms() {
 442     return get_new_prediction(_constant_other_time_ms_seq);
 443   }
 444 
 445   double predict_young_other_time_ms(size_t young_num) {
 446     return
 447       (double) young_num *
 448       get_new_prediction(_young_other_cost_per_region_ms_seq);
 449   }
 450 
 451   double predict_non_young_other_time_ms(size_t non_young_num) {
 452     return
 453       (double) non_young_num *
 454       get_new_prediction(_non_young_other_cost_per_region_ms_seq);
 455   }
 456 
 457   void check_if_region_is_too_expensive(double predicted_time_ms);
 458 
 459   double predict_young_collection_elapsed_time_ms(size_t adjustment);
 460   double predict_base_elapsed_time_ms(size_t pending_cards);
 461   double predict_base_elapsed_time_ms(size_t pending_cards,
 462                                       size_t scanned_cards);
 463   size_t predict_bytes_to_copy(HeapRegion* hr);
 464   double predict_region_elapsed_time_ms(HeapRegion* hr, bool young);
 465 
 466   void start_recording_regions();
 467   void record_cset_region_info(HeapRegion* hr, bool young);
 468   void record_non_young_cset_region(HeapRegion* hr);
 469 
 470   void set_recorded_young_regions(size_t n_regions);
 471   void set_recorded_young_bytes(size_t bytes);
 472   void set_recorded_rs_lengths(size_t rs_lengths);
 473   void set_predicted_bytes_to_copy(size_t bytes);
 474 
 475   void end_recording_regions();
 476 
 477   void record_vtime_diff_ms(double vtime_diff_ms) {
 478     _vtime_diff_ms = vtime_diff_ms;
 479   }
 480 
 481   void record_young_free_cset_time_ms(double time_ms) {
 482     _recorded_young_free_cset_time_ms = time_ms;
 483   }
 484 
 485   void record_non_young_free_cset_time_ms(double time_ms) {
 486     _recorded_non_young_free_cset_time_ms = time_ms;
 487   }
 488 
 489   double predict_young_gc_eff() {
 490     return get_new_neg_prediction(_young_gc_eff_seq);
 491   }
 492 
 493   double predict_survivor_regions_evac_time();
 494 
 495   // </NEW PREDICTION>
 496 
 497   void cset_regions_freed() {
 498     bool propagate = _last_young_gc_full && !_in_marking_window;
 499     _short_lived_surv_rate_group->all_surviving_words_recorded(propagate);
 500     _survivor_surv_rate_group->all_surviving_words_recorded(propagate);
 501     // also call it on any more surv rate groups
 502   }
 503 
 504   void set_known_garbage_bytes(size_t known_garbage_bytes) {
 505     _known_garbage_bytes = known_garbage_bytes;
 506     size_t heap_bytes = _g1->capacity();
 507     _known_garbage_ratio = (double) _known_garbage_bytes / (double) heap_bytes;
 508   }
 509 
 510   void decrease_known_garbage_bytes(size_t known_garbage_bytes) {
 511     guarantee( _known_garbage_bytes >= known_garbage_bytes, "invariant" );
 512 
 513     _known_garbage_bytes -= known_garbage_bytes;
 514     size_t heap_bytes = _g1->capacity();
 515     _known_garbage_ratio = (double) _known_garbage_bytes / (double) heap_bytes;
 516   }
 517 
 518   G1MMUTracker* mmu_tracker() {
 519     return _mmu_tracker;
 520   }
 521 
 522   double max_pause_time_ms() {
 523     return _mmu_tracker->max_gc_time() * 1000.0;
 524   }
 525 
 526   double predict_remark_time_ms() {
 527     return get_new_prediction(_concurrent_mark_remark_times_ms);
 528   }
 529 
 530   double predict_cleanup_time_ms() {
 531     return get_new_prediction(_concurrent_mark_cleanup_times_ms);
 532   }
 533 
 534   // Returns an estimate of the survival rate of the region at yg-age
 535   // "yg_age".
 536   double predict_yg_surv_rate(int age, SurvRateGroup* surv_rate_group) {
 537     TruncatedSeq* seq = surv_rate_group->get_seq(age);
 538     if (seq->num() == 0)
 539       gclog_or_tty->print("BARF! age is %d", age);
 540     guarantee( seq->num() > 0, "invariant" );
 541     double pred = get_new_prediction(seq);
 542     if (pred > 1.0)
 543       pred = 1.0;
 544     return pred;
 545   }
 546 
 547   double predict_yg_surv_rate(int age) {
 548     return predict_yg_surv_rate(age, _short_lived_surv_rate_group);
 549   }
 550 
 551   double accum_yg_surv_rate_pred(int age) {
 552     return _short_lived_surv_rate_group->accum_surv_rate_pred(age);
 553   }
 554 
 555 protected:
 556   void print_stats(int level, const char* str, double value);
 557   void print_stats(int level, const char* str, int value);
 558 
 559   void print_par_stats(int level, const char* str, double* data);
 560   void print_par_sizes(int level, const char* str, double* data);
 561 
 562   void check_other_times(int level,
 563                          NumberSeq* other_times_ms,
 564                          NumberSeq* calc_other_times_ms) const;
 565 
 566   void print_summary (PauseSummary* stats) const;
 567 
 568   void print_summary (int level, const char* str, NumberSeq* seq) const;
 569   void print_summary_sd (int level, const char* str, NumberSeq* seq) const;
 570 
 571   double avg_value (double* data);
 572   double max_value (double* data);
 573   double sum_of_values (double* data);
 574   double max_sum (double* data1, double* data2);
 575 
 576   int _last_satb_drain_processed_buffers;
 577   int _last_update_rs_processed_buffers;
 578   double _last_pause_time_ms;
 579 
 580   size_t _bytes_in_collection_set_before_gc;
 581   size_t _bytes_copied_during_gc;
 582 
 583   // Used to count used bytes in CS.
 584   friend class CountCSClosure;
 585 
 586   // Statistics kept per GC stoppage, pause or full.
 587   TruncatedSeq* _recent_prev_end_times_for_all_gcs_sec;
 588 
 589   // We track markings.
 590   int _num_markings;
 591   double _mark_thread_startup_sec;       // Time at startup of marking thread
 592 
 593   // Add a new GC of the given duration and end time to the record.
 594   void update_recent_gc_times(double end_time_sec, double elapsed_ms);
 595 
 596   // The head of the list (via "next_in_collection_set()") representing the
 597   // current collection set. Set from the incrementally built collection
 598   // set at the start of the pause.
 599   HeapRegion* _collection_set;
 600 
 601   // The number of regions in the collection set. Set from the incrementally
 602   // built collection set at the start of an evacuation pause.
 603   size_t _collection_set_size;
 604 
 605   // The number of bytes in the collection set before the pause. Set from
 606   // the incrementally built collection set at the start of an evacuation
 607   // pause.
 608   size_t _collection_set_bytes_used_before;
 609 
 610   // The associated information that is maintained while the incremental
 611   // collection set is being built with young regions. Used to populate
 612   // the recorded info for the evacuation pause.
 613 
 614   enum CSetBuildType {
 615     Active,             // We are actively building the collection set
 616     Inactive            // We are not actively building the collection set
 617   };
 618 
 619   CSetBuildType _inc_cset_build_state;
 620 
 621   // The head of the incrementally built collection set.
 622   HeapRegion* _inc_cset_head;
 623 
 624   // The tail of the incrementally built collection set.
 625   HeapRegion* _inc_cset_tail;
 626 
 627   // The number of regions in the incrementally built collection set.
 628   // Used to set _collection_set_size at the start of an evacuation
 629   // pause.
 630   size_t _inc_cset_size;
 631 
 632   // Used as the index in the surving young words structure
 633   // which tracks the amount of space, for each young region,
 634   // that survives the pause.
 635   size_t _inc_cset_young_index;
 636 
 637   // The number of bytes in the incrementally built collection set.
 638   // Used to set _collection_set_bytes_used_before at the start of
 639   // an evacuation pause.
 640   size_t _inc_cset_bytes_used_before;
 641 
 642   // Used to record the highest end of heap region in collection set
 643   HeapWord* _inc_cset_max_finger;
 644 
 645   // The number of recorded used bytes in the young regions
 646   // of the collection set. This is the sum of the used() bytes
 647   // of retired young regions in the collection set.
 648   size_t _inc_cset_recorded_young_bytes;
 649 
 650   // The RSet lengths recorded for regions in the collection set
 651   // (updated by the periodic sampling of the regions in the
 652   // young list/collection set).
 653   size_t _inc_cset_recorded_rs_lengths;
 654 
 655   // The predicted elapsed time it will take to collect the regions
 656   // in the collection set (updated by the periodic sampling of the
 657   // regions in the young list/collection set).
 658   double _inc_cset_predicted_elapsed_time_ms;
 659 
 660   // The predicted bytes to copy for the regions in the collection
 661   // set (updated by the periodic sampling of the regions in the
 662   // young list/collection set).
 663   size_t _inc_cset_predicted_bytes_to_copy;
 664 
 665   // Info about marking.
 666   int _n_marks; // Sticky at 2, so we know when we've done at least 2.
 667 
 668   // The number of collection pauses at the end of the last mark.
 669   size_t _n_pauses_at_mark_end;
 670 
 671   // Stash a pointer to the g1 heap.
 672   G1CollectedHeap* _g1;
 673 
 674   // The average time in ms per collection pause, averaged over recent pauses.
 675   double recent_avg_time_for_pauses_ms();
 676 
 677   // The average time in ms for RS scanning, per pause, averaged
 678   // over recent pauses. (Note the RS scanning time for a pause
 679   // is itself an average of the RS scanning time for each worker
 680   // thread.)
 681   double recent_avg_time_for_rs_scan_ms();
 682 
 683   // The number of "recent" GCs recorded in the number sequences
 684   int number_of_recent_gcs();
 685 
 686   // The average survival ratio, computed by the total number of bytes
 687   // suriviving / total number of bytes before collection over the last
 688   // several recent pauses.
 689   double recent_avg_survival_fraction();
 690   // The survival fraction of the most recent pause; if there have been no
 691   // pauses, returns 1.0.
 692   double last_survival_fraction();
 693 
 694   // Returns a "conservative" estimate of the recent survival rate, i.e.,
 695   // one that may be higher than "recent_avg_survival_fraction".
 696   // This is conservative in several ways:
 697   //   If there have been few pauses, it will assume a potential high
 698   //     variance, and err on the side of caution.
 699   //   It puts a lower bound (currently 0.1) on the value it will return.
 700   //   To try to detect phase changes, if the most recent pause ("latest") has a
 701   //     higher-than average ("avg") survival rate, it returns that rate.
 702   // "work" version is a utility function; young is restricted to young regions.
 703   double conservative_avg_survival_fraction_work(double avg,
 704                                                  double latest);
 705 
 706   // The arguments are the two sequences that keep track of the number of bytes
 707   //   surviving and the total number of bytes before collection, resp.,
 708   //   over the last evereal recent pauses
 709   // Returns the survival rate for the category in the most recent pause.
 710   // If there have been no pauses, returns 1.0.
 711   double last_survival_fraction_work(TruncatedSeq* surviving,
 712                                      TruncatedSeq* before);
 713 
 714   // The arguments are the two sequences that keep track of the number of bytes
 715   //   surviving and the total number of bytes before collection, resp.,
 716   //   over the last several recent pauses
 717   // Returns the average survival ration over the last several recent pauses
 718   // If there have been no pauses, return 1.0
 719   double recent_avg_survival_fraction_work(TruncatedSeq* surviving,
 720                                            TruncatedSeq* before);
 721 
 722   double conservative_avg_survival_fraction() {
 723     double avg = recent_avg_survival_fraction();
 724     double latest = last_survival_fraction();
 725     return conservative_avg_survival_fraction_work(avg, latest);
 726   }
 727 
 728   // The ratio of gc time to elapsed time, computed over recent pauses.
 729   double _recent_avg_pause_time_ratio;
 730 
 731   double recent_avg_pause_time_ratio() {
 732     return _recent_avg_pause_time_ratio;
 733   }
 734 
 735   // Number of pauses between concurrent marking.
 736   size_t _pauses_btwn_concurrent_mark;
 737 
 738   size_t _n_marks_since_last_pause;
 739 
 740   // At the end of a pause we check the heap occupancy and we decide
 741   // whether we will start a marking cycle during the next pause. If
 742   // we decide that we want to do that, we will set this parameter to
 743   // true. So, this parameter will stay true between the end of a
 744   // pause and the beginning of a subsequent pause (not necessarily
 745   // the next one, see the comments on the next field) when we decide
 746   // that we will indeed start a marking cycle and do the initial-mark
 747   // work.
 748   volatile bool _initiate_conc_mark_if_possible;
 749 
 750   // If initiate_conc_mark_if_possible() is set at the beginning of a
 751   // pause, it is a suggestion that the pause should start a marking
 752   // cycle by doing the initial-mark work. However, it is possible
 753   // that the concurrent marking thread is still finishing up the
 754   // previous marking cycle (e.g., clearing the next marking
 755   // bitmap). If that is the case we cannot start a new cycle and
 756   // we'll have to wait for the concurrent marking thread to finish
 757   // what it is doing. In this case we will postpone the marking cycle
 758   // initiation decision for the next pause. When we eventually decide
 759   // to start a cycle, we will set _during_initial_mark_pause which
 760   // will stay true until the end of the initial-mark pause and it's
 761   // the condition that indicates that a pause is doing the
 762   // initial-mark work.
 763   volatile bool _during_initial_mark_pause;
 764 
 765   bool _should_revert_to_full_young_gcs;
 766   bool _last_full_young_gc;
 767 
 768   // This set of variables tracks the collector efficiency, in order to
 769   // determine whether we should initiate a new marking.
 770   double _cur_mark_stop_world_time_ms;
 771   double _mark_remark_start_sec;
 772   double _mark_cleanup_start_sec;
 773   double _mark_closure_time_ms;
 774 
 775   // Update the young list target length either by setting it to the
 776   // desired fixed value or by calculating it using G1's pause
 777   // prediction model. If no rs_lengths parameter is passed, predict
 778   // the RS lengths using the prediction model, otherwise use the
 779   // given rs_lengths as the prediction.
 780   void update_young_list_target_length(size_t rs_lengths = (size_t) -1);
 781 
 782   // Calculate and return the minimum desired young list target
 783   // length. This is the minimum desired young list length according
 784   // to the user's inputs.
 785   size_t calculate_young_list_desired_min_length(size_t base_min_length);
 786 
 787   // Calculate and return the maximum desired young list target
 788   // length. This is the maximum desired young list length according
 789   // to the user's inputs.
 790   size_t calculate_young_list_desired_max_length();
 791 
 792   // Calculate and return the maximum young list target length that
 793   // can fit into the pause time goal. The parameters are: rs_lengths
 794   // represent the prediction of how large the young RSet lengths will
 795   // be, base_min_length is the alreay existing number of regions in
 796   // the young list, min_length and max_length are the desired min and
 797   // max young list length according to the user's inputs.
 798   size_t calculate_young_list_target_length(size_t rs_lengths,
 799                                             size_t base_min_length,
 800                                             size_t desired_min_length,
 801                                             size_t desired_max_length);
 802 
 803   // Check whether a given young length (young_length) fits into the
 804   // given target pause time and whether the prediction for the amount
 805   // of objects to be copied for the given length will fit into the
 806   // given free space (expressed by base_free_regions).  It is used by
 807   // calculate_young_list_target_length().
 808   bool predict_will_fit(size_t young_length, double base_time_ms,
 809                         size_t base_free_regions, double target_pause_time_ms);
 810 
 811 public:
 812 
 813   G1CollectorPolicy();
 814 
 815   virtual G1CollectorPolicy* as_g1_policy() { return this; }
 816 
 817   virtual CollectorPolicy::Name kind() {
 818     return CollectorPolicy::G1CollectorPolicyKind;
 819   }
 820 
 821   // Check the current value of the young list RSet lengths and
 822   // compare it against the last prediction. If the current value is
 823   // higher, recalculate the young list target length prediction.
 824   void revise_young_list_target_length_if_necessary();
 825 
 826   size_t bytes_in_collection_set() {
 827     return _bytes_in_collection_set_before_gc;
 828   }
 829 
 830   unsigned calc_gc_alloc_time_stamp() {
 831     return _all_pause_times_ms->num() + 1;
 832   }
 833 
 834   // This should be called after the heap is resized.
 835   void record_new_heap_size(size_t new_number_of_regions);
 836 
 837 protected:
 838 
 839   // Count the number of bytes used in the CS.
 840   void count_CS_bytes_used();
 841 
 842   // Together these do the base cleanup-recording work.  Subclasses might
 843   // want to put something between them.
 844   void record_concurrent_mark_cleanup_end_work1(size_t freed_bytes,
 845                                                 size_t max_live_bytes);
 846   void record_concurrent_mark_cleanup_end_work2();
 847 
 848   void update_young_list_size_using_newratio(size_t number_of_heap_regions);
 849 
 850 public:
 851 
 852   virtual void init();
 853 
 854   // Create jstat counters for the policy.
 855   virtual void initialize_gc_policy_counters();
 856 
 857   virtual HeapWord* mem_allocate_work(size_t size,
 858                                       bool is_tlab,
 859                                       bool* gc_overhead_limit_was_exceeded);
 860 
 861   // This method controls how a collector handles one or more
 862   // of its generations being fully allocated.
 863   virtual HeapWord* satisfy_failed_allocation(size_t size,
 864                                               bool is_tlab);
 865 
 866   BarrierSet::Name barrier_set_name() { return BarrierSet::G1SATBCTLogging; }
 867 
 868   GenRemSet::Name  rem_set_name()     { return GenRemSet::CardTable; }
 869 
 870   // The number of collection pauses so far.
 871   long n_pauses() const { return _n_pauses; }
 872 
 873   // Update the heuristic info to record a collection pause of the given
 874   // start time, where the given number of bytes were used at the start.
 875   // This may involve changing the desired size of a collection set.
 876 
 877   virtual void record_stop_world_start();
 878 
 879   virtual void record_collection_pause_start(double start_time_sec,
 880                                              size_t start_used);
 881 
 882   // Must currently be called while the world is stopped.
 883   void record_concurrent_mark_init_end(double
 884                                            mark_init_elapsed_time_ms);
 885 
 886   void record_mark_closure_time(double mark_closure_time_ms);
 887 
 888   virtual void record_concurrent_mark_remark_start();
 889   virtual void record_concurrent_mark_remark_end();
 890 
 891   virtual void record_concurrent_mark_cleanup_start();
 892   virtual void record_concurrent_mark_cleanup_end(size_t freed_bytes,
 893                                                   size_t max_live_bytes);
 894   virtual void record_concurrent_mark_cleanup_completed();
 895 
 896   virtual void record_concurrent_pause();
 897   virtual void record_concurrent_pause_end();
 898 
 899   virtual void record_collection_pause_end();
 900   void print_heap_transition();
 901 
 902   // Record the fact that a full collection occurred.
 903   virtual void record_full_collection_start();
 904   virtual void record_full_collection_end();
 905 
 906   void record_gc_worker_start_time(int worker_i, double ms) {
 907     _par_last_gc_worker_start_times_ms[worker_i] = ms;
 908   }
 909 
 910   void record_ext_root_scan_time(int worker_i, double ms) {
 911     _par_last_ext_root_scan_times_ms[worker_i] = ms;
 912   }
 913 
 914   void record_mark_stack_scan_time(int worker_i, double ms) {
 915     _par_last_mark_stack_scan_times_ms[worker_i] = ms;
 916   }
 917 
 918   void record_satb_drain_time(double ms) {
 919     _cur_satb_drain_time_ms = ms;
 920     _satb_drain_time_set    = true;
 921   }
 922 
 923   void record_satb_drain_processed_buffers (int processed_buffers) {
 924     _last_satb_drain_processed_buffers = processed_buffers;
 925   }
 926 
 927   void record_mod_union_time(double ms) {
 928     _all_mod_union_times_ms->add(ms);
 929   }
 930 
 931   void record_update_rs_time(int thread, double ms) {
 932     _par_last_update_rs_times_ms[thread] = ms;
 933   }
 934 
 935   void record_update_rs_processed_buffers (int thread,
 936                                            double processed_buffers) {
 937     _par_last_update_rs_processed_buffers[thread] = processed_buffers;
 938   }
 939 
 940   void record_scan_rs_time(int thread, double ms) {
 941     _par_last_scan_rs_times_ms[thread] = ms;
 942   }
 943 
 944   void reset_obj_copy_time(int thread) {
 945     _par_last_obj_copy_times_ms[thread] = 0.0;
 946   }
 947 
 948   void reset_obj_copy_time() {
 949     reset_obj_copy_time(0);
 950   }
 951 
 952   void record_obj_copy_time(int thread, double ms) {
 953     _par_last_obj_copy_times_ms[thread] += ms;
 954   }
 955 
 956   void record_termination(int thread, double ms, size_t attempts) {
 957     _par_last_termination_times_ms[thread] = ms;
 958     _par_last_termination_attempts[thread] = (double) attempts;
 959   }
 960 
 961   void record_gc_worker_end_time(int worker_i, double ms) {
 962     _par_last_gc_worker_end_times_ms[worker_i] = ms;
 963   }
 964 
 965   void record_pause_time_ms(double ms) {
 966     _last_pause_time_ms = ms;
 967   }
 968 
 969   void record_clear_ct_time(double ms) {
 970     _cur_clear_ct_time_ms = ms;
 971   }
 972 
 973   void record_par_time(double ms) {
 974     _cur_collection_par_time_ms = ms;
 975   }
 976 
 977   void record_aux_start_time(int i) {
 978     guarantee(i < _aux_num, "should be within range");
 979     _cur_aux_start_times_ms[i] = os::elapsedTime() * 1000.0;
 980   }
 981 
 982   void record_aux_end_time(int i) {
 983     guarantee(i < _aux_num, "should be within range");
 984     double ms = os::elapsedTime() * 1000.0 - _cur_aux_start_times_ms[i];
 985     _cur_aux_times_set[i] = true;
 986     _cur_aux_times_ms[i] += ms;
 987   }
 988 
 989 #ifndef PRODUCT
 990   void record_cc_clear_time(double ms) {
 991     if (_min_clear_cc_time_ms < 0.0 || ms <= _min_clear_cc_time_ms)
 992       _min_clear_cc_time_ms = ms;
 993     if (_max_clear_cc_time_ms < 0.0 || ms >= _max_clear_cc_time_ms)
 994       _max_clear_cc_time_ms = ms;
 995     _cur_clear_cc_time_ms = ms;
 996     _cum_clear_cc_time_ms += ms;
 997     _num_cc_clears++;
 998   }
 999 #endif
1000 
1001   // Record how much space we copied during a GC. This is typically
1002   // called when a GC alloc region is being retired.
1003   void record_bytes_copied_during_gc(size_t bytes) {
1004     _bytes_copied_during_gc += bytes;
1005   }
1006 
1007   // The amount of space we copied during a GC.
1008   size_t bytes_copied_during_gc() {
1009     return _bytes_copied_during_gc;
1010   }
1011 
1012   // Choose a new collection set.  Marks the chosen regions as being
1013   // "in_collection_set", and links them together.  The head and number of
1014   // the collection set are available via access methods.
1015   virtual void choose_collection_set(double target_pause_time_ms) = 0;
1016 
1017   // The head of the list (via "next_in_collection_set()") representing the
1018   // current collection set.
1019   HeapRegion* collection_set() { return _collection_set; }
1020 
1021   void clear_collection_set() { _collection_set = NULL; }
1022 
1023   // The number of elements in the current collection set.
1024   size_t collection_set_size() { return _collection_set_size; }
1025 
1026   // Add "hr" to the CS.
1027   void add_to_collection_set(HeapRegion* hr);
1028 
1029   // Incremental CSet Support
1030 
1031   // The head of the incrementally built collection set.
1032   HeapRegion* inc_cset_head() { return _inc_cset_head; }
1033 
1034   // The tail of the incrementally built collection set.
1035   HeapRegion* inc_set_tail() { return _inc_cset_tail; }
1036 
1037   // The number of elements in the incrementally built collection set.
1038   size_t inc_cset_size() { return _inc_cset_size; }
1039 
1040   // Initialize incremental collection set info.
1041   void start_incremental_cset_building();
1042 
1043   void clear_incremental_cset() {
1044     _inc_cset_head = NULL;
1045     _inc_cset_tail = NULL;
1046   }
1047 
1048   // Stop adding regions to the incremental collection set
1049   void stop_incremental_cset_building() { _inc_cset_build_state = Inactive; }
1050 
1051   // Add/remove information about hr to the aggregated information
1052   // for the incrementally built collection set.
1053   void add_to_incremental_cset_info(HeapRegion* hr, size_t rs_length);
1054   void remove_from_incremental_cset_info(HeapRegion* hr);
1055 
1056   // Update information about hr in the aggregated information for
1057   // the incrementally built collection set.
1058   void update_incremental_cset_info(HeapRegion* hr, size_t new_rs_length);
1059 
1060 private:
1061   // Update the incremental cset information when adding a region
1062   // (should not be called directly).
1063   void add_region_to_incremental_cset_common(HeapRegion* hr);
1064 
1065 public:
1066   // Add hr to the LHS of the incremental collection set.
1067   void add_region_to_incremental_cset_lhs(HeapRegion* hr);
1068 
1069   // Add hr to the RHS of the incremental collection set.
1070   void add_region_to_incremental_cset_rhs(HeapRegion* hr);
1071 
1072 #ifndef PRODUCT
1073   void print_collection_set(HeapRegion* list_head, outputStream* st);
1074 #endif // !PRODUCT
1075 
1076   bool initiate_conc_mark_if_possible()       { return _initiate_conc_mark_if_possible;  }
1077   void set_initiate_conc_mark_if_possible()   { _initiate_conc_mark_if_possible = true;  }
1078   void clear_initiate_conc_mark_if_possible() { _initiate_conc_mark_if_possible = false; }
1079 
1080   bool during_initial_mark_pause()      { return _during_initial_mark_pause;  }
1081   void set_during_initial_mark_pause()  { _during_initial_mark_pause = true;  }
1082   void clear_during_initial_mark_pause(){ _during_initial_mark_pause = false; }
1083 
1084   // This sets the initiate_conc_mark_if_possible() flag to start a
1085   // new cycle, as long as we are not already in one. It's best if it
1086   // is called during a safepoint when the test whether a cycle is in
1087   // progress or not is stable.
1088   bool force_initial_mark_if_outside_cycle(GCCause::Cause gc_cause);
1089 
1090   // This is called at the very beginning of an evacuation pause (it
1091   // has to be the first thing that the pause does). If
1092   // initiate_conc_mark_if_possible() is true, and the concurrent
1093   // marking thread has completed its work during the previous cycle,
1094   // it will set during_initial_mark_pause() to so that the pause does
1095   // the initial-mark work and start a marking cycle.
1096   void decide_on_conc_mark_initiation();
1097 
1098   // If an expansion would be appropriate, because recent GC overhead had
1099   // exceeded the desired limit, return an amount to expand by.
1100   virtual size_t expansion_amount();
1101 
1102   // note start of mark thread
1103   void note_start_of_mark_thread();
1104 
1105   // The marked bytes of the "r" has changed; reclassify it's desirability
1106   // for marking.  Also asserts that "r" is eligible for a CS.
1107   virtual void note_change_in_marked_bytes(HeapRegion* r) = 0;
1108 
1109 #ifndef PRODUCT
1110   // Check any appropriate marked bytes info, asserting false if
1111   // something's wrong, else returning "true".
1112   virtual bool assertMarkedBytesDataOK() = 0;
1113 #endif
1114 
1115   // Print tracing information.
1116   void print_tracing_info() const;
1117 
1118   // Print stats on young survival ratio
1119   void print_yg_surv_rate_info() const;
1120 
1121   void finished_recalculating_age_indexes(bool is_survivors) {
1122     if (is_survivors) {
1123       _survivor_surv_rate_group->finished_recalculating_age_indexes();
1124     } else {
1125       _short_lived_surv_rate_group->finished_recalculating_age_indexes();
1126     }
1127     // do that for any other surv rate groups
1128   }
1129 
1130   bool is_young_list_full() {
1131     size_t young_list_length = _g1->young_list()->length();
1132     size_t young_list_target_length = _young_list_target_length;
1133     return young_list_length >= young_list_target_length;
1134   }
1135 
1136   bool can_expand_young_list() {
1137     size_t young_list_length = _g1->young_list()->length();
1138     size_t young_list_max_length = _young_list_max_length;
1139     return young_list_length < young_list_max_length;
1140   }
1141 
1142   void update_region_num(bool young);
1143 
1144   bool full_young_gcs() {
1145     return _full_young_gcs;
1146   }
1147   void set_full_young_gcs(bool full_young_gcs) {
1148     _full_young_gcs = full_young_gcs;
1149   }
1150 
1151   bool adaptive_young_list_length() {
1152     return _adaptive_young_list_length;
1153   }
1154   void set_adaptive_young_list_length(bool adaptive_young_list_length) {
1155     _adaptive_young_list_length = adaptive_young_list_length;
1156   }
1157 
1158   inline double get_gc_eff_factor() {
1159     double ratio = _known_garbage_ratio;
1160 
1161     double square = ratio * ratio;
1162     // square = square * square;
1163     double ret = square * 9.0 + 1.0;
1164 #if 0
1165     gclog_or_tty->print_cr("ratio = %1.2lf, ret = %1.2lf", ratio, ret);
1166 #endif // 0
1167     guarantee(0.0 <= ret && ret < 10.0, "invariant!");
1168     return ret;
1169   }
1170 
1171   //
1172   // Survivor regions policy.
1173   //
1174 protected:
1175 
1176   // Current tenuring threshold, set to 0 if the collector reaches the
1177   // maximum amount of suvivors regions.
1178   int _tenuring_threshold;
1179 
1180   // The limit on the number of regions allocated for survivors.
1181   size_t _max_survivor_regions;
1182 
1183   // For reporting purposes.
1184   size_t _eden_bytes_before_gc;
1185   size_t _survivor_bytes_before_gc;
1186   size_t _capacity_before_gc;
1187 
1188   // The amount of survor regions after a collection.
1189   size_t _recorded_survivor_regions;
1190   // List of survivor regions.
1191   HeapRegion* _recorded_survivor_head;
1192   HeapRegion* _recorded_survivor_tail;
1193 
1194   ageTable _survivors_age_table;
1195 
1196 public:
1197 
1198   inline GCAllocPurpose
1199     evacuation_destination(HeapRegion* src_region, int age, size_t word_sz) {
1200       if (age < _tenuring_threshold && src_region->is_young()) {
1201         return GCAllocForSurvived;
1202       } else {
1203         return GCAllocForTenured;
1204       }
1205   }
1206 
1207   inline bool track_object_age(GCAllocPurpose purpose) {
1208     return purpose == GCAllocForSurvived;
1209   }
1210 
1211   static const size_t REGIONS_UNLIMITED = ~(size_t)0;
1212 
1213   size_t max_regions(int purpose);
1214 
1215   // The limit on regions for a particular purpose is reached.
1216   void note_alloc_region_limit_reached(int purpose) {
1217     if (purpose == GCAllocForSurvived) {
1218       _tenuring_threshold = 0;
1219     }
1220   }
1221 
1222   void note_start_adding_survivor_regions() {
1223     _survivor_surv_rate_group->start_adding_regions();
1224   }
1225 
1226   void note_stop_adding_survivor_regions() {
1227     _survivor_surv_rate_group->stop_adding_regions();
1228   }
1229 
1230   void record_survivor_regions(size_t      regions,
1231                                HeapRegion* head,
1232                                HeapRegion* tail) {
1233     _recorded_survivor_regions = regions;
1234     _recorded_survivor_head    = head;
1235     _recorded_survivor_tail    = tail;
1236   }
1237 
1238   size_t recorded_survivor_regions() {
1239     return _recorded_survivor_regions;
1240   }
1241 
1242   void record_thread_age_table(ageTable* age_table)
1243   {
1244     _survivors_age_table.merge_par(age_table);
1245   }
1246 
1247   void update_max_gc_locker_expansion();
1248 
1249   // Calculates survivor space parameters.
1250   void update_survivors_policy();
1251 
1252 };
1253 
1254 // This encapsulates a particular strategy for a g1 Collector.
1255 //
1256 //      Start a concurrent mark when our heap size is n bytes
1257 //            greater then our heap size was at the last concurrent
1258 //            mark.  Where n is a function of the CMSTriggerRatio
1259 //            and the MinHeapFreeRatio.
1260 //
1261 //      Start a g1 collection pause when we have allocated the
1262 //            average number of bytes currently being freed in
1263 //            a collection, but only if it is at least one region
1264 //            full
1265 //
1266 //      Resize Heap based on desired
1267 //      allocation space, where desired allocation space is
1268 //      a function of survival rate and desired future to size.
1269 //
1270 //      Choose collection set by first picking all older regions
1271 //      which have a survival rate which beats our projected young
1272 //      survival rate.  Then fill out the number of needed regions
1273 //      with young regions.
1274 
1275 class G1CollectorPolicy_BestRegionsFirst: public G1CollectorPolicy {
1276   CollectionSetChooser* _collectionSetChooser;
1277 
1278   virtual void choose_collection_set(double target_pause_time_ms);
1279   virtual void record_collection_pause_start(double start_time_sec,
1280                                              size_t start_used);
1281   virtual void record_concurrent_mark_cleanup_end(size_t freed_bytes,
1282                                                   size_t max_live_bytes);
1283   virtual void record_full_collection_end();
1284 
1285 public:
1286   G1CollectorPolicy_BestRegionsFirst() {
1287     _collectionSetChooser = new CollectionSetChooser();
1288   }
1289   void record_collection_pause_end();
1290   // This is not needed any more, after the CSet choosing code was
1291   // changed to use the pause prediction work. But let's leave the
1292   // hook in just in case.
1293   void note_change_in_marked_bytes(HeapRegion* r) { }
1294 #ifndef PRODUCT
1295   bool assertMarkedBytesDataOK();
1296 #endif
1297 };
1298 
1299 // This should move to some place more general...
1300 
1301 // If we have "n" measurements, and we've kept track of their "sum" and the
1302 // "sum_of_squares" of the measurements, this returns the variance of the
1303 // sequence.
1304 inline double variance(int n, double sum_of_squares, double sum) {
1305   double n_d = (double)n;
1306   double avg = sum/n_d;
1307   return (sum_of_squares - 2.0 * avg * sum + n_d * avg * avg) / n_d;
1308 }
1309 
1310 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTORPOLICY_HPP